The increasing development of industrial mass-produced parts with photocatalytically active, self-cleaning and antibacterial properties demands ever more precise, more rapid and more automated measuring methods. In the past, new measuring methods were thus developed with which it is possible to examine the surfaces of photocatalytic materials made of glass, plastic material, metal, wood or even textile woven fabrics for their self-cleaning and/or antibacterial properties during irradiation with UV light and also with light of the visible spectrum. Whilst the most current but easy to handle methods based on transmission- or absorption measurements of coloured aqueous solutions (e.g. methylene blue decomposition; DE 10 2005 011 219) deliver generally only qualitative results with very long measuring times, the precise application of thin layers of organic test substances directly on the surfaces makes possible extremely rapid and above all also quantitative evaluation of the photocatalytic activity.
DE 10 2004 027 118 describes a method for quantitative determination of the photocatalytic decomposition of organic colourants or colourant-containing algal and bacterial strains on photocatalytically active surfaces by means of fluorescence analysis. For this purpose, the samples to be tested are coated with organic colourants or colourant-containing substances. Subsequently, the samples are irradiated with UV or visible light of known intensity and spectral distribution and their fluorescence intensity is detected by means of fluorescence scanners, chip readers or a fluorescence microscope. The thereby resulting reduction in fluorescence of the colour-coated photocatalyst in comparison with a jointly coated but photocatalytically inactive reference thereby applies as a measure of the photocatalytic efficiency of the sample to be tested.
DE 10 2006 049 009.6 describes a measuring method for measuring the photocatalytic activity of surfaces by scattered light measurement on thin fatty acid layers. For this purpose, the surfaces to be measured are evaporated with thin stearic acid layers, as a result of which a homogeneous scattering surface is produced. The surface is subsequently irradiated with UV light and the light component scattered by the stearic acid layer (haze) is thereby measured at defined time intervals. If the surface is photocatalytically active, then the applied layer decomposes without residue so that the optical haze drops to the value of the uncoated surface. From the time-dependent curve course of the optical haze, the quantitative photocatalytic activity of the sample can hence be determined.
In contrast to other known photocatalytic measuring methods, DE 10 2004 027 118 and DE 10 2006 049 009 describe two novel measuring principles with a high throughput and with simultaneously high precision, as a result of which firstly exact and reproducible, quantitative determinations of the photocatalytic efficiency of different photocatalytically active surfaces could be produced with low complexity. Both methods hereby use different test substances (e.g. fluorescent colourants or organic fatty acids) so that different optical aids are required for acquiring the measuring values in the individual case. Whilst in fluorescence measurement of colourants, fluorescence scanners, chip readers or fluorescence microscopes can be used, there are required for scattered light measurement on the stearic acid layers, a haze meter, a gloss measuring device or a spectral photometer with connected integration sphere. Because of the different measuring geometries or the light sources required for the measurement, both methods cannot hence readily be combined with each other. Furthermore, according to the current state of research, no commercially available device is in a position to produce a quantitative analysis of photocatalytic activity with simultaneous irradiation in the UV or visible spectral range.